Reasons for TCH Blocking:
Some of them are-
High Utilization of TCH
Time slot faulty.
Lock TRXs.
HW Problem.

Solutions for removal of TCH Blocking:
Implement half rate or Dual rate.
Check FRL & FRU.
Add another TRX. If TRX addition not possible, try to share the traffic of that cell with the neighboring cell by changing tilt or orientation.